A Long Term Evolution (LTE) system is based on an orthogonal frequency division multiple access (OFDMA) technology. A time-frequency resource is divided into OFDM symbols in a time domain dimension and OFDM subcarriers in a frequency domain dimension. A minimum resource granularity is referred to as a resource element (RE), indicating a time-frequency grid formed by one OFDM symbol in the time domain and one OFDM subcarrier in the frequency domain. In the LTE system, a service is transmitted based on scheduling by a base station. A specific scheduling process is as follows: A base station sends a control channel, where the control channel may carry scheduling information of a physical downlink shared channel (PDSCH) or a physical uplink shared channel (PUSCH), and the scheduling information includes control information such as resource allocation information and a modulation and coding scheme; and a UE receives a downlink data channel or sends an uplink data channel according to the scheduling information carried in the control channel. Herein, the PDSCH is equivalent to the downlink data channel, and the PUSCH is equivalent to the uplink data channel. Generally, the base station implements scheduling for the user equipment (UE) on a per resource block pair (RBP) basis. A resource block pair occupies a length of one subframe in the time domain, and occupies a width of 12 OFDM subcarriers in the frequency domain. One subframe generally includes 14 OFDM symbols.
To maintain service transmission or perform cell selection, reselection, or handover, the UE needs to perform synchronization, cell identification, and a radio resource management (RRM) measurement according to a reference signal sent by the base station. The RRM measurement includes a measurement of a reference signal received power (RSRP), reference signal received quality (RSRQ), a received signal strength indicator (RSSI), and the like. A reference signal used to implement the foregoing functions in a current small cell is referred to as a discovery reference signal (DRS), specifically including a primary synchronization signal (PSS), a secondary synchronization signal (SSS), and a cell-specific reference signal (CRS). The PSS and the SSS are mainly used for cell synchronization and cell identification, and the CRS is used for RRM measurement. Certainly, the UE may use the CRS to implement cell identification, or the like. FIG. 1 shows a schematic diagram of resource locations of a DRS in a resource block. In the prior art, a minimum sending period of a DRS is 40 ms. Specifically, the DRS is sent within a sending time window appearing every 40 ms, and the sending time window is referred to as a DRS measurement timing configuration (DMTC). Duration of the DMTC is generally 6 ms, and a PSS/SSS in the DRS needs to be sent in a subframe 0 and/or a subframe 5 in the DMTC. It can be seen that the DRS occupies discontinuous OFDM symbols in a subframe. In other words, CRSs are sent on symbols 0, 4, 7, and 11, the PSS/SSS is sent on symbols 5 and 6, and other symbols do not carry the DRS currently.
Frequency spectrums deployed in a serving cell of the existing LTE system are all licensed spectrums, that is, a frequency spectrum can be used only by an operator network for which the frequency spectrum has been purchased. An unlicensed spectrum is attracting increasing attention. Because the unlicensed spectrum does not need to be purchased and can be used by any operator and organization, a specific rule needs to be complied with, to resolve a problem of coexistence of different parties using the unlicensed spectrum. The rule may be referred to as a listen before talk (LBT) rule. Specifically, before sending a signal on a channel of a U-LTE serving cell, a base station needs to perform a clear channel assessment (CCA) on the channel of the serving cell. Once a detected receive power exceeds a threshold, the base station cannot send a signal on the channel temporarily. The base station cannot send a signal on the channel until detecting that the channel is idle. Alternatively, in some cases, the base station further needs to back off for a random period of time. The base station can send a signal on the channel only when the channel remains idle within the backoff time.
Considering that the existing DRS occupies discontinuous OFDM symbols in a subframe, it is not suitable to transmit the DRS on an unlicensed spectrum. This is because other stations in another system or in a same system may detect on idle OFDM symbols that the channel is idle, and then send signals. Consequently, a conflict and interference are generated between the signals sent by these stations and the sent DRS, and problems such as RRM measurement inaccuracy are also caused. Therefore, to send a DRS on the unlicensed spectrum, continuous OFDM symbols need to be occupied. As a result, resource locations of the DRS on the unlicensed spectrum are inconsistent with those of the existing DRS. In addition, another factor that needs to be considered is: The current DRS can be sent only in the subframe 0 and the subframe 5 in the DMTC. This limits opportunities to send the DRS in the DMTC on the unlicensed spectrum. For example, the station learns that the channel is idle on a subframe 1, but the DRS cannot be sent at this time. Therefore, it is necessary to allow the DRS to be sent in a subframe in the DMTC different from the subframe 0 and the subframe 5. The change of the resource locations and a sending mechanism of the DRS on the unlicensed spectrum affects, to some extent, resource reuse occurred when the DRS and a normal control channel and data channel are sent together in a subframe.